Ideally a wound dressing should adhere tightly and protect the wound from outside foreign matter, liquids and microorganisms. It should draw out exudate as it forms, while not totality desiccating the wound. Also the dressing should control the wound gas microenvironment during healing by allowing ingress of oxygen and egress of carbon dioxide at the appropriate rates. Many wound dressings are known that achieve a number of these properties.
U.S. Pat. Nos. 4,598,004; 3,645,835; 4,638,797; 4,600,001; and 4,413,621 describe wound dressings that function very well for shallow wounds with relatively low exudate levels. However, in general they are not ideal for highly exudative wounds, because they do not avoid exudate pooling under the dressing. Low exudate removal rate hydrogel dressings are also disclosed in U.S. Pat. Nos. 4,554,317; 3,419,006 3,993,551 and 3,664,343.
U.S. Pat. Nos. 4,645,624; 4,499,896 and 4,657,006 disclose pouch dressings that provide better exudate management. These dressings, however generally have poor skin adherence and do not handle the large volumes of exudate.
U.S. Pat. Nos. 3,972,328, 4,538,603, and EP 0,190,814 describe dressings consisting of rubber-based adhesives compounded with various absorbent materials, covered with impermeable film or foam sheets. These dressings absorb and hold the exudate. If left in place on highly exudative wounds, a significant amount of fluid is entrapped next to the wound, building up a significant undesirable pressure. These occlusive dressings often leak the entrapped fluid.
U.S. Pat. Nos. 4,477,325 and 4,738,257 describe modified occlusive rubber dressings that have decreased degradation of the rubber into the wound because of crosslinking of the rubber. Decreased skin adhesion results from the crosslinking, so that the dressings tend to leak exudate.
Many types of island dressings have been developed to better handle exudate. These island dressings have highly absorbent pads and transmit moisture vapor to the air. See U.S. Pat. Nos. 4,753,231; 4,181,127; 4,561,435 and 4,649,909. These dressings are not entirely satisfactory because of inadequate moisture vapor transmission to handle very high exudative wounds, and/or inadequate control of wound/gas environment.
Several patents disclose island dressings having some structural similarities to the dressings of the present invention. U.S. Pat. No. 4,231,357 discloses an island dressing having an absorbent pad in a liquid pervious envelope. This dressing relies on dressing changes, rather than moisture vaporization, for exudate removal. Leakage through the permeable envelope is a serious problem. The dressing does not attempt to deal with the wound gas microenvironment. U.S. Pat. No. 4,641,643 and EP 0236104 disclose island dressings having fenestrated base layers that may have therein an absorbent pad. The dressing of the U.S. Patent has a transparent film cover sheet that is hinged at one end so that it can be raised to give access to the wound for cleansing and medication. These references contain no disclosure concerning control of gas microenvironment.
A number of dressings have been described that are designed primarily for exudate removal. See EP 106,439; 106,440; and 174,803. These dressings do not enable the changing of the wound gas microenvironment without changing the entire dressing. They do not comprise a base layer that remains on the patient through a number of dressing changes. While these dressings can be used for low exudative wounds, they are not ideal for highly exudative wounds. Not only is exudate handling generally insufficient, but also these prior art dressings are not capable of controlling and varying the gas levels of the wound environment as healing progresses through wound healing phases.
Wound classification by stages is conventional. A Stage I wound is a shallow wound that penetrates into but not through the epidermis. A Stage II wound penetrates through the epidermis, and possibly into some subcutaneous tissue like fat, but not into muscle or bone.
Stages I and II type wound healing can be considered to take place through three healing phases. During initial Phase 1 of healing, high exudate withdrawal and high oxygen concentration are desirable. Phase 1 continues until angiogenesis has begun to restore blood flow to the wound.
During Phase 2, fibroblast migration and proliferation begin the generation of collagen and basement growth. Less exudate removal, but even greater concentrations of oxygen are desirable. This phase continues until re-epithelization has started.
The final Phase 3 of the wound healing involves the continuation and completion of re-epithelization, and wound approximation and closure. Low exudate removal is involved, but a very high oxygen concentration is desirable.
During the curing of Stage I and/or Stage II type wounds, a number of dressing changes normally are required during each healing phase, and different gas and water vapor permeabilities are desirable in each phase to provide appropriate wound microenvironments. Removal of the wound dressings from the site may damage the wound peripheral skin. It is therefore desirable to minimize the number of complete dressing changes, while being able to modify the wound microenvironment.
A wound dressing has been discovered that greatly minimizes the number of times the dressings must be removed from the skin, while enabling the modification of the dressing permeabilities during the healing process, thereby changing the wound microenvironment.